Coolant systems, such as those used in automobiles, commonly use a coolant fluid concentrate comprising an alcohol, such as ethylene glycol, which is usually diluted with water when used in the coolant system. The alcohol/water mixture is corrosive to the metals, such as steel, cast iron, brass, copper, lead/tin solders, and aluminum, in which the coolant comes in contact during operation of the coolant system. In order to prevent corrosion of these metals, there have been a wide variety of corrosion inhibitors added to the coolant fluid concentrate to retard the corrosion of the metallic surfaces in contact with the coolant fluid. In addition, pH buffers are frequently added to maintain a basic pH to prevent acid corrosion. Therefore, an effective corrosion inhibitor additive must maintain its corrosion inhibitory effect at a basic pH value. Also because of the wide variety of metals and alloys used in an automobile coolant system, the corrosion inhibitor additive should be noncorrosive to all the metals present and not lessen the noncorrosive properties of other constituents that may also be present in the coolant. Many corrosion inhibitors have been suggested to inhibit the corrosion of one or more metals found in a coolant system. These include guanadine, citrates, coal tar derivatives, petroleum bases, thiocyanates, peptones, phenols, thioureas, tannin, quinoline, morpholine, triethanolamine tartrates, glycol mono-ricinoleate, organic nitrites, mercaptans, sulfonated hydrocarbons, fatty oils, triazoles, mercaptobenzothiazoles, phenothiazine, piperazine, sulfates, sulfides, fluorides, hydrogen peroxide, alkali metal chromates, nitrites, phosphates, borates, tungstates, molybdates, carbonates, silicates, silicones and silicate-silicone copolymers.
In modern automobile coolant systems there is a wider use of solders with a higher lead content, as high as about 95 percent lead or greater, as compared with formerly used alloys which have a lead content of about 70 weight percent lead. Under corrosive conditions, the higher lead solders are susceptible to the formation of "solder bloom", which is the accumulation of corrosion products of lead upon the solder surface. Since these corrosion products remain in-situ and have a much higher volume than the original lead solder, solder bloom accumulation can result in a significant lowering of the cross-sectional area and restriction of the smaller heat exchange openings. This in turn causes a significant decrease in the heat-exchange capacity of the coolant system and eventual overheating of the internal combustion engine.
Solder bloom corrosion was not considered a serious problem until the middle 1960's when higher lead solders began to commonly appear in automotive heat exchange systems. Solder blood accumulation is typically nonexistent or insignificant in heat exchange systems using the lower 70 weight percent lead content solders, thus until the use of solder with a lead content equal to or greater than about 95 weight percent became prevalent, solder bloom corrosion in automobile coolant systems was not generally significant. As the use of high lead solders has increased, the number of cars that are susceptible to serious solder bloom corrosion has also increased. There is, therefore, a continuing need for a coolant composition that inhibits the formation of solder bloom.
Because of the different metals used in a coolant system, it is important that a solder bloom inhibitor not be corrosive toward other metals, in particular aluminum. Aluminum now is used in increasing frequency in the construction of engine blocks, heads, radiators, and the like. This use of aluminum has presented new problems due to the aluminum coming in contact with the coolant fluid. Aluminum tends to corrode at hot heat exchange surfaces in the block and the head to form soluble corrosion products. These soluble corrosion products then precipitate at cooler surfaces in the heat exchange system where their concentration exceeds their solubility. The resulting precipitate deposits can then accumulate to an extent to restrict the openings for fluid flow in the radiator core, cover the inner heat exchange surface of the radiator, and thereby lower the cooling efficiency of the cooling system. It is desirable, therefore, that an antifreeze concentrate inhibit corrosion towards aluminum and not significantly interfere with the corrosion inhibitory function of other additives that may be present.
Antimony compounds have been known to act as corrosion inhibitors for steel in acid solutions. For example, Mago et al. in U.S. Pat. No. 3,808,140 disclose the use of antimony compounds as corrosion inhibitors of steel exposed to alkanolamine solutions employed in acid gas removal service. As disclosed by Mago et al., antimony compounds inhibit the acid corrosion of ferrous metals in carbonate solutions. (See col 2, lines 7 to 15).
Schwartz in U.S. Pat. No. 2,303,399 discloses an alkali detergent used for cleaning soft metal such as aluminum and tin. Added to the detergent is an antimony salt to reduce the corrosive effect of the solution. The detergent cleaning solutions are essentially oxygenated solutions of water, and corrosion would result from interaction of the dissolved oxygen and water to dissolve or corrode the metal (see col. 1, line 36).
Berliner et al. in U.S. Pat. No. 1,915,148 disclose an antifreeze composition for inhibiting the corrosion of oxidizable metals which comprises a lower aliphatic alcohol (methanol, ethanol, propanol) and a tartrate compound such as an alkali tartrate, alkaline earth tartrate, or antimony alkali tartrate. Since the tartrate compounds are more soluble in water, they are preferably dissolved first in water which is then subsequently added to the alcohol.
An object of the invention is to provide a coolant composition that inhibits corrosion from metal surfaces in automobile cooling systems, in particular a composition that inhibits solder bloom corrosion on lead solder surfaces.
It is also an object of the invention to provide a corrosion inhibitor that is compatible with the components of current coolant compositions.